Seismic data acquisition may be conducted by towing some number of streamer sections behind a vessel. The streamer sections may have varying types of construction and sensor mounting in the streamer. Data recorded on these streamers are stored in memory on the towing vessel.
Ocean bottom cable (“OBC”) is another recording body used in seismic data acquisition. OBC differs from towed marine because the cables remain stationary on the sea floor and the data may be recorded either on a dedicated recording buoy or a recording vessel.
In both cases the length of cable sections is on the order of 100 m. The sections are connected together to make streamer lengths of up to 12 km. Cables of this length require electrical power to record and transmit data along the length of the cables. Further, the recording systems dedicated to store the acquired seismic data are complex and require well trained seismic observers to manage the acquisition and perform quality control of the data.
OBC surveys are between 3 and 5 times as expensive as towed marine surveys due to the time required to acquire the data. A vessel and trained crew is needed to deploy the cable and attach the data and power transmission cable to a buoy to be ready for data recording. This may take a considerable amount of time.
Towed marine streamer spreads may consist of between 6 and 12 streamers and are seldom shorter in length than 3 km. The large size of these spreads makes controlling the streamer locations difficult especially in the presence of ocean currents. This lack of control results in difficulty in maneuvering near stationary production platforms.
Full waveform inversion (“FWI”) is a seismic inversion method used to derive an earth model from seismic data. The current FWI technology enables inversion for compressional velocities (Vp) and some anisotropic parameters, for example, Thompson's parameters (epsilon and delta). Long offset data (e.g., more than 12 km) or ultra-long offset data (e.g., more than 20 km) and very low frequencies (e.g., less than 3 Hz) are required for FWI to generate accurate velocity models. Acquisition of long and ultra-long offset towed-streamer marine seismic data is expensive, as this may involve very long streamers or additional source vessels.